Fix another instance of "created at"
Fix another instance of "created at"

Replace it with "created on".

Change-Id: Ibd26bf82d2e64f142a4f3be6da7701e5b035602f

8thcolor/eurucamp2014-htdsadr,8thcolor/rubyconfau2015-sadr,8thcolor/rubyconfau2015-sadr,8thcolor/eurucamp2014-htdsadr,8thcolor/eurucamp2014-htdsadr,8thcolor/rubyconfau2015-sadr